1. Field of the Invention
The present invention relates to a sample setting method and an apparatus for setting the sample into a vaporizer of a premixing chamber and, more particularly, for microsampling method for transferring a minute sample thereinto.
2. Description of the Background Art
When the amount of the sample is small as in the case of a bio-sample, it is difficult to transfer the sample by a continuous suction method for transferring the sample continuously via a tube into a flame type atomic absorption spectrophotometer. In such a case, the sample is transferred by a microsampling method.
FIG. 14 shows a flame type atomic absorption spectrophotometer provided with an apparatus for transferring the sample by the aforementioned sampling method. The premixing chamber 270 has in its base portion a vaporizer 216 by which the sample injected is vaporized by air supplied from a capillary 272, at the same time a fuel gas and air are mixed with the vaporized sample. The vaporized sample 274 mixed with the fuel gas and air is led to a burner head 276 of the chamber 270 and is atomized in a flame 278. Reference numeral 280 represents an optical axis of an optical flux.
In the microsampling method is used a funnel-shaped sample receiver 212 to facilitate injection of the sample. This sample receiver 212 has an upward opening and a hole at its bottom, and is connected via tube 214 to the capillary 272.
A sample 284 is dripped into the sample receiver 212 by means of a sample injection nozzle 282. When the burner is burning with a flame, the sample supplied to the sample receiver 212 is sucked by negative pressure into the vaporizer 216 and is vaporized before it enters into the burner.
When in the microsampling method the sample injecting rate into the sample receiver 212 is lower than the suction rate of the vaporizer 216, there results a phenomenon of the supply of the sample 284 being interrupted as shown in FIG. 15. This interruption results in wild fluctuation of the atomic absorption waveform, as shown in FIG. 5 (A), and in the deterioration of the measuring precision.
In case there is a risk of interference caused by coexisting materials in the flame type atomic absorption analysis, it is often possible to reduce measuring errors through matrix modification or by adoption of the so-called standard addition method. In such a case it is necessary to do a pretreatment such as adding a reagent or standard sample to an unknown sample or sometimes to dilute an unknown sample with a blank solution. In a calibration curve method, too, a pretreatment in which the standard sample is diluted stepwise to prepare a series of standard sample solutions diluted generally integer-fold is necessary.
In the flame type atomic absorption analysis method such pretreatment is currently being done by the operator.
Meanwhile, in some types of flameless type atomic absorption spectrophotometer, pretreatment is done automatically by the use of a pretreating apparatus, and solutions to be measured are sucked serially and continuously and are injected at once into a graphite furnace to be atomized. In the flameless type of analysis it is sometimes the case that even if the individual solutions are not thoroughly mixed in the pretreating process such solutions are mixed to some extent by diffusion in the graphite furnace to enable precise analysis. In the flame type of analysis, however, when the solutions sucked serially and continuously by the use of the pretreating apparatus for flameless type analysis are supplied to the vaporizer as they are, the samples are atomized in the order they are supplied, hence there is no meaning of pretreatment.